This relates generally to imaging devices, and more particularly, to imaging devices having compact image sensor pixels with high dynamic range functionalities.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. Typical image sensors contain image pixels that include a photodiode for generating charge in response to incident light. Image sensors can operate using a global shutter or a rolling shutter scheme. In a global shutter scheme, every image pixel in the image sensor simultaneously captures an image, whereas in a rolling shutter each row of image pixels sequentially captures an image.
An image sensor has an associated dynamic range, which is expressed as a ratio of the largest and smallest possible luminance values for the image sensor. Image sensors are often equipped with high dynamic range (HDR) functionality, in which the image sensors capture images at extended dynamic ranges beyond what would otherwise be possible using image sensors without HDR functionality. One of the most common HDR techniques is multiple exposure imaging. In multiple exposure imaging, multiple images are captured with an image sensor at different exposure times and are later combined into a high dynamic range image. However, as the multiple exposures are captured at different times, it can be difficult to correctly capture images of moving objects. In addition, if care is not taken while performing HDR imaging, the image pixels in the image sensor can saturate and limit the signal-to-noise ratio of the final image.
It would therefore be desirable to be able to provide imaging devices with improved image sensor pixels.